Crossfeed scavenging for multi-cylinder two cycle engines



c. n. SWAN@ CROSSFEED SCAVENGING FOR MULTI-"CYLINDER TWO CYCLE ENGINES Dec 6, i966 Filed April 27, 1964 CARBURETOR CARBURETOR CARBURETOR !N\ ENTOR CHARLES D. SWAN@ BY jin dr'US gi Star/QQ ffmveys United States Patent 3,289,656 CROSSFEEB SCAVENGING FOR MULTI- CYLINDER TWO CYCLE ENGllNE Charles D. Strang, Gshkosli, Wis., assigner to Kiekhaefer Corporation, Fond du Lac, Wis., a corporation of Dela- Wre Filed Apr. 27, 1964, ser. No. 362,567 s claims. (ci. 12s-59) This invention relates to crossfeed scavenging for multi-cylinder two cycle engines.

Heretofore, in the construction of multi-cylinder two cycle internal combustion engines it has been the practice to supply the fuel-air mixture for each cylinder solely from the crankcase for that cyclinder.

In a crankcase-scavenged two-cycle internal combustion engine, the fuel-air mixture for each cylinder passes from the carburetor through as uitable valve means and into the crankcase for that cylinder while the piston is ascending. As the piston descends this mixture in the corresponding crankcase is compressed.

As the piston approaches the bottom end of its stroke, it uncovers exhaust ports in the cylinder wall and thereby permits the burned charge in the cylinder to exhaust through these ports.

Further descent of the piston uncovers intake ports in the cylinder wall which are connected by transfer passages to the crankcase, to thereby permit the compressed fuel-air mixture in the crankcase to enter the cylinder through the intake ports and push out any remaining burned gases, a process referred to as scavenging The objective is to iill the cylinder with a fresh charge of fuel-air mixture as free of burned gases as possible.

It is sometimes desirable to delay entry of a portion of the charge into the cylinder until after the initial charge has effected the scavenging action. In this way the major portion of the fuel-air mixture in the crankcase is used for scavenging the cylinder in the normal manner, and then after a short delay, a final portion of the mixture is admitted through the same or different intake ports. By this means the ow of the gases within the cylinder may be controlled or altered to obtain maximum discharge of exhaust gases and maximum retention of the fresh charge.

When the piston rst uncovers the intake ports, the transfer of the fuel-air mixture from the crankcase to the cylinder takes place very rapidly, and it is dicult to retain a sufficient portion of the mixture at a pressure suitable for the delayed charging of the cylinder.

The present invention is based upon the concept that when there are a plurality of cylinders with a common crankshaft as in a multicylinder engine it is possible to solve the problem by providing a cross feed of fuel-air mixture from a crankcase of one cylinder to another cylinder and to time this cross feed by the uncovering of a port in either cylinder by the piston movement therein at the right time in its stroke.

The accompanying drawing illusrates the best mode presently contemplated for carrying out the invention.

ln the drawing:

FIGURE l is an exploded schematic view of a four cylinder engine in which each cylinder is separately sec tioned longitudinally thereof and normal to the crankshaft, and schematically showing the crossfeed passages interconnecting the same;

FIG. 2 is a transverse section of one of the cylinders taken on line 2 2 of FIG. l to show an arrangement for the ports; and

FIG. 3 is a view similar to FIG. l showing a different type of crossfeed.

The invention is illustrated as applied to a four cylinder engine in which the cylinders A, B, C and D have a firing order of A, C, B, and D, and the pistons 1 are greatest Patented Dec., 6, 1966 connected to the crankshaft 2 at 90 apart in the order of firing.

The pistons 1 operate in corresponding individual cylinders 3 which are mounted on the crankcase 4 of the engine. The crankcase 4 is partitioned transversely between the adjacent cylinders to provide in effect a separate crankcase chamber 5 for each cylinder.

A fuel-air mixture is applied to each crankcase chamber 5 from the carburetor 6, shown only schematically, during the period when the corresponding piston 1 is moving upwardly into its cylinder and in effect the crankcase chamber is expanding. Suitable valve means, not shown, closes the passages for fuel-air mixture from each carburetor 6 to the corresponding chambers during the period when the corresponding piston 1 is moving downwardly into the crankcase and the crankcase chamber is in effect contracting.

Each cylinder 3 is provided with one or more primary fuel inlet ports 7 in the side walls thereof and which connect openly with the corresponding crankcase chamber 5 at all times through the transfer passages 3. The ports 7 are disposed at a position relative to the piston movement where they will be uncovered by the piston and thereby admit a charge of fuel-air mixture to the cylinder from the pressurized crankcase chamber at a time when the piston is near the bottom of its stroke. The ports 7 are covered by the corresponding piston to close the same at all other periods ofthe cycle.

Each cylinder 3 is provided with one or more exhaust ports 9 in the wall of the cylinder, and which are disposed to be closed by the piston during the compression and ring strokes of the piston and to be uncovered for free exhaust of the burned gases from the cylinder just prior to the opening of the primary inlet ports 7 of the downward stroke of the piston.

Suitable `ignition means 10 are provided to ignite the compressed charge of fuel-air mixture within each cylinder in the usual manner when the piston is near the top of the stroke and the resulting explosion drives the piston downwardly and thereby drives the crankshaft of the engine.

As the hot gases in the cylinder expand and force the piston downwardly the piston reaches the location where it uncovers the corresponding exhaust port 9 and the spent gases then escape from the cylinder. Almost immediately thereafter the piston uncovers the inlet ports 7 admitting a fresh charge of fuel-air mixture -to the cylinder 3 from the corresponding crankcase chamber 5. The ports 7 and 9 are generally so related and directed as to cause the rush of incoming fuel-air mixture through ports 7 to flow Iin a manner that forces the spent gases from .the cylinder through the port 9, a process known as scavenging In general it is ydesired not to have any of the fresh charge of fuel-air mixture escape through the exhaust port 9 vbefore the latter is closed by upward movement of the piston 1, and at the same time it is desired that as little .as possible of the spent ygases should be entrapped Iin the cylinder at the time the exhaust port 9 is closed. Various engine `designs have been developed and may be employed to provide a maximum efficiency in this respect,

Due to the pressure of harmonics and transient waves involved in the rapid exchange of a fresh charge for the spent charge Within the cylinder, it has been found that the spent Agases are not fully purged from the cylinder and certain `losses in eciency inevitably result therefrom. Some appreciation may be had of this problem when it is realized that the time period for a single exchange is in fact iniinitesimal for an engine operating at 4000 revolutions per minute. It is in fact amazing that the gas flows involved can take place as rapidly as needed for such high speed engines.

The present invention provides a means for modifying the pressure involved in the gas flows by separating the charging of the gases into the cylinder into two or more separate and distinct periods with a very minute time delay therebetween, and thereby effecting a sustained gas flow for a given time.

In carrying out Ithe invention, a second small charge of fuel-air mixture is admitted to each cylinder from the crankcase for another cylinder in which the fuel-air mixture is at the time under moderate pressure, at a point in the downward stroke of the piston just after at least partial scavenging of the cylinder by the charge entering through the primary inlet ports 7. For this purpose in the embodiment of FIG. 1, each cylinder 3 is provided with a secondary inlet port 11 which is disposed to be uncovered just after ports 7 are uncovered and only at the bottom increment of the piston stroke.

The port 11 for each cylinder is connected by a transfer passage 12 to the crankcase chamber 5 for the cylinder following in point of ring order.

Thus the port 11 for cylinder A is connected by its transfer passage 12 to the crankcase chamber 5 for cylinder C; the port 11 for cylinder C is connected by its transfer passage 12 to the crankcase chamber 5 for cylinder B; the port 11 for cylinder B -is connected by its transfer passage 12 to the crankcase chamber 5 for the cylinder D; and the port 11 for cylinder D is connected by its `transfer passage to the crankcase chamber 5 for cylinder A.

After the piston 1 in cylinder A has uncovered the corresponding ports 7 and the gases from the corresponding crankcase chamber 5 have entered the cylinder as a primary charge to effect scavenging, the piston 1 then uncovers port 11 and thereby lets a small charge of fresh fuel-air mixture to enter the cylinder A from the crankcase chamber 5 of cylinder C. At this time the piston 1 for cylinder C is in its downward firing stroke and has partially compressed the fuel-air mixture in the crankcase chamber 5 for cylinder C. The port 11 will remain open only a moment until piston 1 in cylinder A passes the bottom of its stroke and rises to close off the port.

Thus the cylinder A will take away a small amount of the prospective charge for cylinder C, but the total charge for each cylinder will be equal and in fact the same as it would have been without crossfeed, since cylinder C will in turn receive a similar delayed small charge from the crankcase chamber 5 of cylinder B, cylinder B will in turn receive a similar delayed small charge from the crankcase chamber 5 of cylinder D, and cylinder D will in turn receive a similar delayed small charge from the crankcase chamber 5 of cylinder A, all in the sequence of firing of the cylinders.

The invention in effect divides the charge into a lgiven cylinder into two impulses and thereby counteracts certain pressure characteristics in the cylinder and/ or at the exhaust port and provides a sustained charging flow of gas over a longer period whereby a more complete scavenging is effected and a more efficient engine operation is obtained.

In the embodiment of FIGURE l the ports 11 are solely controlled by the piston in each corresponding cylinder since the transfer passages 12 are openly connected at all times -to their corresponding crankcase chambers 5. This necessitates having the ports 11 separate from ports 7.

In the embodiment of FIG. 3 the ports 7 function as the inlet for both the primary and secondary charges of fuel-air mixture to the corresponding cylinder. This is accomplished by having each secondary transfer passages 13, which provides the crossfeed, connect with the corresponding transfer passage 8 to effect its discharge through the port 7.

The other end of each seconda-ry .transfer passage 13 is connected to the corresponding crankcase chamber 5 through a port 14 in the'wall of the cylinder and a second port or opening 15 through the skirt of the corresponding piston for receiving and transmitting the secondary charge of fuel-air mixture only at a time when the piston is moving down in its firing stroke. Thus the timing for the secondary charge can provide the desired time delay relative to the primary charge admitted to a given cylinder.

More specifically, as illustrated in FIG. 3, yshortly after `the piston in cylinder A has uncovered port 7 and admitted the primary charge to the cylinder from its crankcase chamber 5, the piston in cylinder C in its downward movement effects momentary registration of ports 14 and 15 thereby supplying a secondary charge from the crankcase chamber 5 of cylinder C through ports 15 and 14 and through the corresponding passage 13 and port 7 into cylinder A. By the time the piston in cylinder C on its upward stroke again registers the ports 14 and 15, the piston in cylinder A has covered and closed port 7 so that no flow of gas mixture will occur from crankcase chamber 5 in cylinder C through the passage 13 except at the desired time of feed.

The above explanation applies equally well with respect to the crossfeed for a secondary charge of fuel-air mixture from the crankcase chamber 5 of the cylinder B to the port 7 of cylinder C, from the crankcase chamber 5 of cylinder D to the port 7 of cylinder B, and from the crankcase chamber 5 of cylinder A to the port 7 of cylinder D.

With this embodiment of FIG. 3 it is desirable to provide a check valve 16, preferably of the reed valve type, in each passage 13 to prevent possible Iback ow of gases therethrough at the time ports 14 and 15 register on the upstroke of the piston, since the opposite end of the passage is freely connected to the other crankcase chamber through passage 8. This particular requirement would be avoided if passage 13 were to feed a port in the cylinder wall separate from port 7, similar to the way passage 12 in FIG. l feeds to port 11.

This embodiment provides an excellent control of the amount and timing of the secondary charge for each cylinder and prevents possible undue loss of fuel mixture from the crankcase chambers prior to the primary scavenging of the cor-responding cylinders.

In the illustrations of both embodiments of FIG. 1 and FIG. 3, the arrows in the passages 12 and 13 indicate the direction of flow of fuel mixture at the time the delayed secondary charge is provided for the corresponding recipient cylinders.

The invention, *by providing separate primary and secondary fuel charges to each cylinder in effect gives a prolonged or sustained scavenging action that substantially improves the eficiency of the engine.

Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing out and distinctively claiming the subject matter which is regarded as the invention.

I claim:

1. In a two cycle internal combustion engine comprising a plurality of cylinders having individual pistons connected to a common crank shaft at different angles to provide avdetermined sequence of firing for the cylinders, a separate crankcase chamber for each cylinder and ported thereto for supplying a fuel-air lmixture from the chamber to the cylinder under the control of the piston movement in the cylinder, means to supply a fuelair mixture to said crankcase chambers during the cornpression stroke for the corresponding pistons, and exhaust ports in the walls of said cylinders and disposed to be uncovered by the corresponding pistons as they approach the end of the firing stroke to discharge spent gases from the cylinder, the intake port or ports from each crankcase chamber to its correspon-ding cylinder -being disposed in the wall of the cylinder and relative to said exhaust port or ports therefor to be uncovered by the corresponding piston at a time after opening of the exhaust ports whereby a primary charge of fuel-air mixture entering the cylinder scavenges the same by driving most of the spent gases therefrom; the improvement comprising xmeans connecting each cylinder with the crankcase chamber for the cylinder next to iire in the firing sequence, and means to close each said connecting means at all times except for a moment after opening of said intake port or ports by the piston.

2. The construction of claim 1 in which said connecting means for each cylinder comprises a transfer passage discharging through at least one port in the wall of the cylinder, and said closing means comprises the [piston for said cylinder and which uncovers the port or ports after the piston has at `least partially uncovered the first named port or ports.

3. The construction of claim 1 in which said connecting means is connected to its crankcase chamber by a port through the Wall of the corresponding cylinder and a registering port in the `skirt of the corresponding piston, and the opposite end of said connecting means is connected to its cylinder through a port controlled by the piston therein, whereby crossfeed occurs through said connecting means only at a time when both pistons have uncovered their respective ports and said connecting means is closed by at least one of said pistons at other times in the cycle.

4. The construction of claim 3 in which the said opposite end of said connecting means discharges into the transfer passage for the intake port of the corresponding cylinder, and a check valve is provided in said connecting means to prevent back flow of gases therethrough from one crankcase chamber to the other upon registering of said skirt and cylinder ports during the return stroke of the piston.

5. The improvement in multi-cylinder two cycle internal combustion engines employing crankcase fuel feed through conventional transfer passages between the crankcase chambers and their corresponding cylinders, comprising a crossfeed passage for fuel-air mixture from the crankcase chamber for each cylinder to the cylinder immediately ahead in firing sequence, and means to open each said passage momentarily during scavenging of the cylinder into which it discharges.

6. The improvement in multi-cylinder two cycle internal combustion engines employing crankcase fuel feed through conventional transfer passages 'between the crankcase chambers and their corresponding cylinders comprising passage means discharging a minimal amount of fuel-air mixture into each cylinder at a delayed time relative to initial scavenging of the cylinder, each said passage means -being connected to receive said mixture from the crankcase chamber of another cylinder wherein the piston is at said time in its firing stroke.

References Cited by the Examiner UNITED STATES PATENTS 1,632,684 6/1927 Tuckeld 123--59 1,722,951 7/1929 Barkey 123-59 1,845,177 2/1932 Pal-rn 12? 59 2,833,255 5/1958 Lejardi 123-59 3,105,474 10/1963 Kiekhaefer 123-59 3,132,635 5/1964 Heidner 123-73 MARK NEWMAN, Primary Examinez'.

WENDELL E. BURNS, Examiner. 

5. THE IMPROVEMENT IN MULTI-CYLINDER TWO CYCLE INTERNAL COMBUSTION ENGINES EMPLOYING CRANKCASE FUEL FEED THROUGH CONVENTIONAL TRANSFER PASSAGES BETWEEN THE CRANKCASE CHAMBERS AND THEIR CORRESPONDING CYLINDERS, COMPRISING A CROSSFEED PASSAGE FOR FUEL-AIR MIXTURE FROM THE CRANKCASE CHAMBER FOR EACH CYLINDER TO THE CYLINDER IMMEDIATELY AHEAD IN FIRING SEQUENCE, AND MEANS TO OPEN EACH SAID PASSAGE MOMENTARILY DURING SCAVENGING OF THE CYLINDER INTO WHICH IT DISCHARGES. 